System and method for dissolving gases in liquids

ABSTRACT

Apparatus and methods for dissolving a gas into a liquid comprises a saturation tank, a high pressure liquid pump in fluid communication with the tank, and a pressurized gas source in communication with a regulated gas head space of the saturation tank. The saturation tank comprises a pressure vessel for containing the liquid and has a regulated gas head space above the liquid, contains at least one liquid spray nozzle that permits passage of liquid into the pressure vessel, and an outlet for the liquid containing dissolved gas. Upon passing the gas-containing liquid into a second fluid, the gas is released in the form of microbubbles. The microbubbles aid in flocculation of suspended particles and promote dissolution of the gas in the second fluid. Preferred gases for use with the apparatus are oxygen, air, and ozone. Anticipated uses include treatment of rivers, streams, and ponds in natural or industrial settings, as well as smaller scale applications.

REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/574,152, filed May 25, 2004, the disclosure of which is incorporatedherein by reference.

STATEMENT OF GOVERNMENT SUPPORT

The present invention has been supported at least in part by U.S.SeaGrant Agency No. 502048. Further development of the technology hasbeen supported by the National Science Foundation SBIR program, GrantNo. DMI-0419555. The Government may have certain rights in theinvention.

FIELD OF THE INVENTION

The present invention relates to methods and apparatus for dissolvinggases in liquids. The invention particularly relates to oxygenation andozonation of municipal, industrial, residential and environmental watersupplies, bulk gas exchange and control in industrial andbiotechnological processes, and applications to manufacturing,distribution and control of nanoparticles and related technologies.

BACKGROUND OF THE INVENTION

Many different systems and methods, depending on application, areavailable for dissolving gases in liquids. Some of the main applicationsare for the oxygenation of outdoor water bodies, industrial uses, andthe treatment of wastewater.

The aeration/oxygenation of water in outdoor settings is necessary forthe remediation of local environments subjected to high oxygen demandloads. Typical devices used to oxygenate water bodies are based onentraining atmospheric air into the top surface layer through fountainsor paddle-type rotating wheels; or submersion entrainment with diffusersor bubble aerators that pump air to the bottom of the water body andallow bubbles to rise to the surface. Drop structures that createwaterfalls also employ the same process of entrainment. These devicesare typically operated continuously and are permanently installedequipment with high capital costs.

Many devices also exist for oxygenating water in an industrial settingsuch as vortex entrainment technology and equipment from severaldifferent manufacturers, including Air Products (Allentown, Pa.) and AirLiquide (Paris, France), but this type of equipment is usually notappropriate for field use because of high capital costs and theinability to operate continuously in outdoor conditions at remotelocations. These devices are also typically not appropriate for highparticulate water because of sensitivity to clogging.

Most of the current products and techniques for oxygenation of waterwere developed for large-scale wastewater treatment. The requiredequipment is usually permanently installed, installation istime-intensive, and there are high capital and start-up costs. Becausemost of the products available for oxygenation are not portable, theflexibility of their applications is quite limited. Wastewater treatmentplants use two basic methods to aerate wastewater: entrainment or airvia diffusers or other aeration devices; and, mechanical agitation toentrain air from the atmosphere into the water.

Entrainment diffusers create air bubbles by pumping air directly intothe liquid phase through diffusers or some other type of device. Themost widely used diffusers are classified as either porous or fine pore(nonporous). Porous diffusers incorporate porous ceramic tubing/platethrough which air passes, creating very small bubbles that aerate thewater. Diffusers that are classified as nonporous use perforated pipingor tubing for introducing air to water. Other types of diffusers includejet aerators, aspirators, and U-tube aerators.

Mechanical aerators usually employ impellors and may be fixed orfloat-mounted. They may be classified as high-speed axial-flow pumptype, slow-speed vertical turbine, submerged slow-speed turbine withsparger ring, and rotating brush. In pump-type aerators, which are usedprimarily in aeration lagoons, oxygen is transferred as the spray passesthrough the air and the area where turbulence is created around theimpellers. The slow-speed vertical turbine blades, used for activatedsludge, aerobic digesters, and aerated lagoons, are submerged a fewinches below the water surface where air entrapment occurs in thevicinity of the turbine. Compressed air is released below the turbinewith the submerged slow-speed vertical turbine with sparger ring tocreate oxygen transfer. Finally, the rotating brush, used mainly inoxidation ditches, is a long horizontal axle with radiating steelbristles that are partly submerged. Air transfer occurs in the immediatevicinity of the bristles.

Another type of aeration treatment technique is a stabilization pond (oroxidation pond), which is a relatively shallow body of wastewatercontained in an earthen basin and used for secondary treatment ofsettled wastewater. Oxygen is introduced through wind mixing, mechanicalaerators, or photosynthetic processes. In the stabilization pond,organic matter is stabilized through the combined action of algae andother microorganisms. Algae produce oxygen while growing in the presenceof sunlight. This resultant oxygen is then used by other microbes foroxidizing organic matter, which in turn results in carbon dioxide,ammonia, and phosphates as end products. These end-products are requiredby algae for growth, resulting in a cyclical process and stabilizationbecause of these combined processes. Stabilization ponds are classifiedas aerobic, facultative (aerobic-anaerobic), and anaerobic. An aeratedlagoon is similar to an aerobic pond, but it is usually deeper, andoxygen is introduced via mechanical aerators rather than photosyntheticoxygen production.

Another process that can add oxygen to water is Dissolved Air Flotation(DAF), which was initially designed for solids flotation. In DAF, anenclosed container of water and air are compressed, thereby dissolvingthe air into the water. The pressure on the batch is then suddenlyreleased and the air comes out of solution. Microbubbles are formed thatattach to solids and nutrients in the water and float them to thesurface. DAF is usually a batch process within settling and skimmingtanks. Although not usually considered a method for oxygenation, DAF maybe useful as an oxygenation technique.

Air flotation involves forming bubbles by introducing the gas phasedirectly into the liquid through impellers or diffusers. A DAF systemundergoes the following processes: The influent is mixed with coagulantsto cause flocculation or the formation of larger particles. This usuallyincludes a rapid redox shift using ferric chloride or similar reducingagents, often with acrylic acid to enhance flocculation of fine solids.A recycle stream of effluent water is pressurized and saturated with airin the saturation tank, then added to the flocculated influent. Thismixture is then released into the contact zone where the microbubbles(<100-120 μm) come out of solution under the lower pressure and attachto the flocculants, forming bubble-floc agglomerates. These agglomeratesthen leave the contact zone and rise to the surface of the flotationtank, forming a floating sludge layer on the surface of the water. Thissludge is then removed by a mechanical surface scraper.

Most dissolved air flotation systems consist of similar components andcan include coagulant mixing for flocculation, a saturated recyclestream, a contact zone, and a flotation tank. Others use a pilot plantwith a static mixer, flocculation chamber, flotation chamber, saturatorwith recycle stream, and a filter column. Early stage DAF plants usuallyconsist of a chemical coagulation area, flocculator, flotation tank,saturator, and a recycle stream.

Methods of gas saturation in a liquid include sparging air into thewater in a pressure vessel, trickling the water over a packed bed,spraying the water into an unpacked saturator, entraining air withejectors, and injecting air into the suction pipe of the recycle pump.Typical saturators are operated between 50 to 85 psig with bubble sizedecreasing as saturator pressure increases. Also, the retention timewill increase as bubble size decreases. It is found that smaller bubblesresult in a slower rise velocity as well as a smaller contact anglebetween bubble and particle, therefore increasing the possibility ofcollision between particle and bubble.

Discussion of Patent References

U.S. Pat. No. 5,979,363 (issued to Shaar) describes an aquaculturesystem that involves piping a food and oxygen slurry into a pond. U.S.Pat. No. 5,911,870 (issued to Hough) proposes a device for increasingthe quantity of dissolved oxygen in water and employs an electrolyticcell to generate the oxygen. U.S. Pat. No. 5,904,851 (issued to Tayloret al.) proposes a method for enriching water with oxygen that employs aturbulent mixer to entrain the gas in the liquid. U.S. Pat. No.5,885,467 (issued to Zelenak et al.) proposes mixing a liquid withoxygen using a plurality of plates or trays over which the liquid flowsgradually downward. U.S. Pat. No. 4,501,664 (issued to Heil et al.)proposes a device for treating organic wastewater with dissolved oxygenthat employs several process compartments. U.S. Pat. No. 5,766,484(issued to Petit et al.) proposes a dissolved gas flotation system fortreatment of wastewater wherein the relative location of inlet andoutlet structures reportedly maximizes the effect of air bubbles inseparating solids from the fluid. U.S. Pat. No. 5,647,977 (issued toArnaud) proposes a system for treating wastewater that includesaeration, mixing/flocculating, and contact media for removing suspendedsolids, etc. U.S. Pat. No. 5,382,358 (issued to Yeh) proposes anapparatus for separation of suspended matter in a liquid by dissolvedair flotation (DAF). U.S. Pat. No. 3,932,282 (issued to Ettelt) proposesa dissolved air flotation system that includes a vertical flotationcolumn designed with an aim of preventing bubble breakage.

An object of the present invention is to provide a simplified, low costmethod and apparatus for rapidly increasing the dissolved gas levels ina liquid. A further object of the invention is to provide a method offloating particles suspended in the fluid.

SUMMARY OF THE INVENTION

Apparatus and methods are disclosed for facilitating dissolution of oneor more gases into a liquid, such as water. Preferred gases for use withthe apparatus are oxygen, air, and ozone, and preferred applicationsinclude oxygenation and/or ozonation treatment of rivers, streams, andponds in natural, municipal, or industrial settings.

An apparatus of the present invention comprises a saturation tank, ameans of transporting the liquid into the saturation tank, and apressurized gas source in communication with the saturation tank. Thesaturation tank comprises a pressure vessel for containing the liquidand affords a regulated gas head space over the liquid in the vessel.The saturation tank is preferably further provided with at least oneliquid spray nozzle that permits passage of the liquid into the pressurevessel in the head space region of the tank. The saturation tank also isprovided with an outlet for the liquid containing dissolved gas, whichpermits it to exit the tank and to pass into an external fluid having alower partial pressure of the gas. Only the liquid exits the device—allgases are contained in the saturation tank and only exit the saturationtank dissolved in liquid. Once the supersaturated liquid is contactedwith the external fluid, gas dissolved in the liquid at a higher partialpressure is released in the form of microbubbles. The microbubblespromote dissolution of the gas in the external fluid and can aid inflocculation and flotation of any suspended particles therein.

A method of dissolving a gas in a liquid comprises pressurizing anenclosed vessel with the gas, spraying a first portion of the liquidinto the vessel containing the gas under conditions effective todissolve the gas in the liquid, passing the first portion of liquidcontaining dissolved gas from the vessel into a chamber that is providedwith a plurality of orifices and which is immersed in a second portionof the liquid, and discharging the first liquid portion containingdissolved gas into the second liquid portion under conditions effectiveto form microbubbles of the gas in the second liquid portion at or nearthe chamber orifices. Microbubbles on the order of 150 micron diameteror less (including nanobubbles) can be obtained by a method of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram for treatment of a natural stream witha generic gas using a microbubble generation device of the presentinvention.

FIG. 2 shows the rate of O₂ added per energy (g/min/kW) delivered by afield scale unit as a function of spray nozzle size and pressure insidea saturation tank. Theoretical energy consumed is a measure of theenergy required to deliver oxygen and is independent of motorefficiency. (solid line ♦=1 nozzle, long dash line ▪=2 nozzles, shortdash line ▴=3 nozzles, long dash short dash line X=4 nozzles).

FIG. 3 shows the effect of backpressure due to nozzle type (♦=largenozzles from field-scale unit vs. ●=small nozzles from lab-scale unit onpercent saturation of water in the saturation chamber. Water that is100% saturated at the elevated pressure in the saturation chamber (atthe pressure set point) would be supersaturated at atmospheric pressure.

FIG. 4 depicts DO levels as a function of time for different operatingregimens (♦=present invention: “Eco-Oxygenator”; ▪=fine-bubble oxygen:oxygen bubbled into bottom of tank using typical diffuser; ▴=fine-bubbleair: air bubbled into bottom of tank using typical diffuser. TheEco-Oxygenator quickly raised DO levels and each peak in its line showsthat when the device is turned on the DO level rises quickly, whichpermits the device to be turned off for the majority of each hour.

FIG. 5 illustrates relative DO levels vs. time for three technologies(X=present invention: “Eco-Oxygenator”; ♦=Agitator R1: typical surfaceagitation using submerged impeller with air entrainment; ▴=DropStructR1: commonly used entrainment by pumping water to height above watersurface and dropping water stream into surface, causing entrainment).

DETAILED DESCRIPTION OF THE INVENTION

The present invention is for methods and apparatus for dissolving a gasin a liquid. An object of the invention is to raise the concentration ofa dissolved gas in a target fluid body by discharging into it a liquidhaving the gas dissolved therein at a higher partial pressure. To thisend, a liquid is preferably prepared with the gas at or near saturationlevels at a pressure higher than that of the target liquid.

As shown in FIG. 1, one embodiment of the invention comprises saturationtank 2 and liquid pumping means 4 in fluid communication with thesaturation tank. The pumping means receives liquid from stream 6 viafilter 8 and supply tank 10. A source 12 of the gas is in communicationwith the saturation tank. Saturation tank 2 preferably comprisespressure vessel 14 for containing the liquid 16 and providing a gas headspace 18 above the liquid at a super-atmospheric pressure. Thesaturation tank also comprises at least one liquid spray nozzle 20 thatpermits passage of liquid into the pressure vessel through action ofpumping means 4. The saturation tank also comprises an outlet 22 in thetank that permits passage of gasified liquid into external chamber 24,through connecting means 26, where it is discharged into liquid stream 6by passing through a plurality of orifices provided in the wall of theexternal chamber (not shown). Microbubbles 28 are thereby released intothe stream.

Whenever the partial pressure of the gas in the target fluid isinitially lower than that of the gas dissolved in the liquid coming fromthe saturation tank, the concentration of dissolved gas in the targetfluid is increased. Preferably, the size, shape and number of orificesin the external chamber are predefined so that microbubbles of gas areformed at or near the chamber orifices, thereby enhancing dissolution ofthe gas in the target fluid. The gas is preferably air, oxygen, ozone,hydrogen, nitrogen, nitrous oxide, or carbon dioxide, and the liquid istypically composed primarily of water.

A pumping means of the present invention is suitably selected from among(i) a high pressure liquid pump, (ii) a line source, such as tap water,in a residential or industrial setting, or (iii) a plurality of fixedvolume vessels capable of forcing liquid into the saturation tank uponpressurization of the fixed vessel with a high pressure gas that entersthe vessel and displaces the liquid through an outlet in the vessel. Formost outdoor applications, a high pressure pump is convenientlyselected. Many commercial sources are available with the ratingdepending on application, as is readily apparent to the skilledpractitioner.

A gas dissolution system of the present invention can be operated inbatch or continuous mode. Whenever the system is operated in continuousmode, it is preferred that the ratio of liquid volume to head space gasvolume in the saturation tank is maintained, which can be done using anopen-loop or closed-loop control system.

A source of gas is also a component of the system and depends upon thetype and amount of gas required for an application. Air can be pumpeddirectly from the atmosphere into the saturation tank in someapplications. In others, bottled oxygen, obtained cryogenically, oroxygen separated from the atmosphere on-site can be used. In such latterapplications, it may be preferable to employ a non-cryogenic means forpurifying oxygen from ambient air. Non-cryogenic equipment for purifyingoxygen can be obtained commercially, such as from Universal IndustrialGases, Inc. (Easton, Pa.). In still other applications, ozone can beprovided, typically by on-site generation of ozone from oxygen or air.Such ozone generators can be obtained commercially from SpartanEnvironmental Technologies, Inc. (Mentor, Ohio). The ozone generator canbe installed conveniently within the saturation tank.

Liquid in the saturation tank is contacted with a gas or gases of choicefor a predetermined period of time sufficient to bring liquid to or nearsaturation with the gas. Next, the liquid containing dissolved gas ispassed into the external chamber, which is provided with a plurality oforifices. Under continuous operation, the number, size, and placement oforifices in the chamber are preferably predefined so as to permit therate of liquid flow rate out of the chamber to balance the rate ofliquid flow into the saturation tank, thereby maintaining constantpressure internal the saturation tank under constant flow conditions.Additionally, the chamber, which is conveniently tube-shaped, can beprovided internal a liquid entrainment means, such as a hollow tube, sothat the liquid containing dissolved gas exiting the chamber mixesthoroughly with the lower pressure target fluid. It is preferred thatmicrobubbles generated by the system have an average diameter less thanabout 150 microns, and in certain applications nano-bubbles having anaverage diameter in the range of about 10 nm to about 100 nm arepreferred.

Determination of the number, size and placement of the orifices in thechamber wall, as well as the pumping means, gas pressure in the tank,and liquid flow rate into and out of the tank, can be determined byengineering design calculation and/or on-site calibration through trialand error. Alternatively, it may be preferred to make adjustments from aknown set of parameters by making considerations for viscosity, density,and surface tension of the liquid so as to optimize the ratio of gasdelivered to energy consumed for a given application. Additionally, itmay be desired to regulate the gas saturation threshold for the liquidby thermally controlling the saturation tank. Moreover, it may bepreferred to employ adjustable spray nozzles within the saturation tankso as to optimize the liquid droplet size and control the rate of gassaturation in the liquid.

A system of the present invention can further comprise an electroniccontrol system for controlling its operation, e.g., by controlling pumpspeed, gas pressure, valve operation, and the like. The apparatus canfurther comprise a feedback loop that permits recovery and recycling ofthe gas to the saturation tank.

The present invention further contemplates a novel method of dissolvinga gas in a liquid. Such method comprises pressurizing an enclosed vesselwith the gas, spraying a first portion of the liquid into the vesselcontaining the gas under conditions effective to dissolve the gas in theliquid, passing the first portion of liquid containing dissolved gasfrom the vessel into a chamber that is provided with a plurality oforifices and which is immersed in a second portion of the liquid, anddischarging the first liquid portion containing dissolved gas into thesecond liquid portion under conditions effective to form microbubbles ofthe gas in the second liquid portion at or near the chamber orifices.

Such a method of the invention can be employed with any, or acombination, of the gases air, oxygen, ozone, hydrogen, nitrogen,nitrous oxide, and carbon dioxide. Conventionally, the liquid primarilycomprises water, and may contain significant levels of suspendedparticles. In a method of dissolution, the portion of the liquid at highpressure within the saturation tank is preferably dissolved with gas to95% or greater of saturation, resulting in supersaturation (2000% orgreater of saturation) of the liquid after discharge to near atmosphericpressure conditions. Accordingly, whenever the gas-containing liquid isdischarged into the second portion of liquid, microbubbles having anaverage diameter less than about 150 microns are formed and releasedinto the fluid. Typically, the gas employed is air or oxygen, and theliquid to be gasified is water in a natural or wastewater setting. Anoxygen source is preferably obtained by commercial cryogenic methods. Inanother preferred embodiment of the invention, the gas is ozone and theliquid is water to be purified for home, medical, or municipal use. Theozone can be provided by on-site generation, and preferably enters thesaturation tank at or near ambient pressure, where it is pressurized viaa closed system injection of liquid until a desired higher pressure isattained prior to discharge of the gas-containing liquid.

To promote intimate contact of liquid and gas, the liquid is preferablysprayed into the saturation tank under pressure provided by a highpressure liquid pump. To ensure proper tank pressure and outflow rates,fluid flow into the saturation tank from a high pressure pump iscontrolled via feedback from sensors indicating water capacity withinthe saturation tank.

Representative applications of the present technology include thefollowing:

-   enhance microbe growth and respiration rate in waste water    treatment, fermentation processes, food synthesis and manufacturing,    or solid waste treatment;-   promote physical flotation of matter suspended in the liquid;-   quench anaerobic biological activity in the liquid;-   produce nanobubbles (10-100 nm diameter);-   foam a polymer;-   create a biorefuge for attracting or sustaining fish populations;-   sterilize a body of water;-   facilitate surface freezing while aerating during cold weather;-   to control odor, antibiotic residuals, and/or bacterial loads in    sewage transport conduits;-   improve the quality of water entering, transducing, or exiting a    dam;-   improving aerobic digestion efficiency and/or odor control in a    wastewater treatment pond (lagoon);-   respond to a pollutant spill into an environmental water body;-   isolate and/or treat a plume of pollution;-   disinfect and reduce organic carbon in drinking water;-   control aerobic and anaerobic conditions in biological processes    associated with pharmaceuticals and biotechnology;-   deliver hydrogen or other gases to create and control aerobic and    anaerobic conditions in biological processes associated with in situ    waste treatment in groundwater;-   deliver hydrogen or other gases to create and control aerobic and    anaerobic conditions in biological processes associated with in situ    waste treatment in surface waters;-   deliver a high concentration of dissolved oxygen to enhance    biological oxidation of organic carbon and nitrogen removal within    wastewater treatment facilities;-   oxidize sediment in situ for enhanced bioremediation of contaminants    sorbed to and associated with river, lake, and estuarine sediments;-   enhance oxygen treatment of refractory pollutants such as antibiotic    residuals, endocrine disruptors, pesticides, and similar chemicals;-   enhance ozone treatment of refractory pollutants such as antibiotic    residuals, endocrine disruptors, pesticides, and similar chemicals;-   inject supersaturated stream of oxygen, ozone, hydrogen or other    gases for direct treatment or enhancing treatment of groundwater to    remove pollutants;-   increase the rate of BOD removal because of improved treatment rate    from smaller bubble size; and-   increase the thickness of the aerobic layer in sediment for increase    storage capacity of phosphorus or other water pollutants.    I: Aeration and Oxygenation of Water

A principal aspect of the present invention is a new approach foreffectively and efficiently dissolving gases into a water/wastewatermatrix. The primary reason for dissolving gases like air and oxygen intoliquids like water is to increase the rates of biologically-mediatedprocesses such as organic waste assimilation, biochemical processcontrol, and ecosystem respiration.

In a major aspect of the invention, oxygen (O₂) is provided to aquaticecosystems at the molecular and microbubble level, thereby enhancinghydrolysis, microbial metabolism, and oxidation. This system provides anenvironmentally benign alternative for in situ treatment of organics,phosphorus, and anaerobic byproducts (ammonia, methane, hydrogensulfide). The ability to add oxygen to a water body can lead to improvedecosystem health, increased aesthetic value of the water system,increased rate of natural pollutant removal, and increased assimilationcapacity, which means increasing the organic and phosphorus loads awater body can receive. Specifically, this technology can provide an insitu (or on site) intervention for remediating many important sources ofwater pollution.

In another aspect of the invention, ozone (O₃) is provided to waterbodies to oxidize biological and chemical pollutants to render the watersafe for human contact and consumption.

The present invention is based on the principle that the amount of gasthat can be dissolved into water depends upon an equilibrium solubility,which increases as the partial pressure of the gas in contact with thewater increases. By increasing the partial pressure of the gas to highlevels, the amount of gas dissolved into the water dramaticallyincreases. The invention uses this principle to create a carrier streamof water that contains high concentrations of gas that is supersaturatedin the water at standard atmospheric pressure. The carrier stream isthen injected at the site where the oxygen/ozone/gas is needed. Thecarrier stream of supersaturated water is decompressed as it moves frominside the device to outside at the point of treatment. Thisdecompression results in the equilibrium solubility of the gas in thecarrier stream being reduced which results in the gas exiting solutionas very small bubbles (microbubbles). The microbubbles are thendistributed throughout the system into which the carrier stream has beeninjected where they quickly redissolve. The carrier stream can deliverconcentrations on the order of 245 ppm oxygen to waters requiring 7 ppmoxygen, therefore, a relatively small amount of water is required todeliver gas to a larger amount of fluid. In some applications, the fluidbeing treated can be continually circulated through the device so thereis no net addition of water to the system. The behavior of themicrobubbles after injection into the system is a function of theproperties of the system—in systems with low gas concentration, theyquickly redissolve, whereas in systems that are saturated, they largelyremain formed as microbubbles.

The advantage of using pressure to dissolve gas into a carrier stream ofliquid is that the dissolution process is conducted within the deviceunder favorable conditions for fast and efficient dissolution as opposedto most technologies that conduct dissolution at the point of treatment.Another advantage is that the high pressure in the device creates veryhigh gas concentrations resulting in very high gradients between thecarrier stream and the fluid being treated. Manyoxygenation/aeration/ozonation processes are limited by the diffusionrate of the gas to the fluid being treated. Diffusion rate is controlledby dissolved gas concentration gradient between the injection site andwater requiring the gas. As the gradient increases, so to does thediffusion rate. This results in faster delivery of dissolved gas to thesite where it is required.

Use of high pressure to dissolve gas into water would appear moreexpensive than dissolving gas into water at low pressure because energymust be added to compress the gas and fluid to the high pressure.However, high pressure dissolution results in much more gas beingdissolved into the water such that the high pressure system can be morecost-effective on the basis of rate of dissolved gas delivered per costof energy.

By using a carrier stream of water to deliver the dissolved gas, muchmore precise control of dissolved gas delivery rate can be realized asthe amount of gas dissolved into the carrier stream at a constantpressure is very consistent and controllable as there are constantphysical mechanisms controlling the rate and amount of gas in thecarrier stream. The rate of dissolved gas being delivered is directlycontrolled by controlling water delivery rate, which can be veryaccurately controlled.

For instance, for a 50 gallon capacity saturation tank, an inlet liquidflow rate of 32 gallons per minute through one spray nozzle and an inletoxygen flow rate of 1.36 scfm charge the liquid carrier stream to 95%saturation at 110 psi saturation tank pressure, which corresponds to3774% of saturation at standard atmospheric pressure under continuousflow operation conditions, where the exit flow rate of oxygen-containingliquid is 32 gallons per minute and the rate of oxygen delivery to thetarget water is 32 grams per minute of water with a concentration of 260mg oxygen per liter of water.

It is preferred also that the exit flow rate of liquid from the externalchamber matches the flow rate into the saturation tank, in which casethe total cross-sectional area of the orifices in the chamber coupledwith the flow rate of water entering the saturation chamber results in apressure loss across the orifices equal to the desired pressure in thesaturation tank. Preferred orifice diameters are in the range of 1 mm to15 mm in order to ensure that the gas does not prematurely emerge fromsolution, allowing the formation of microbubbles in the target water.Orifice size also controls exit water velocity, direction and mixingcharacteristics between the carrier stream of supersaturated water andtarget water being treated. Such a system can be scaled as desired for agiven application, which is readily within the capability of the skilledpractitioner.

Depending upon the rate of dissolved gas that must be delivered, thedevice is relatively small and portable and can therefore be used atremote locations outdoors. Its portability allows the device to be ableto treat many different locations without a permanently fixedinstallation. Larger demands can be delivered using skid-mounted,truck-mounted, or floor-mounted systems.

The device not only delivers water saturated with gas, but also providesthe added benefit of microbubbles of the dissolved gas as it comes outof solution once injected into the water. Microbubbles can attachdirectly to particulate matter in the water. These particles includeorganic matter and the bacteria that are typically the source of oxygenconsumption and responsible high oxygen demand. Thus, the deviceprovides the additional benefit of allowing directedaeration/oxygenation/ozonation within the fluid being treated.

Microbubbles are far more effective than larger size bubbles used instandard bubble aeration technology because the high surfacearea-to-volume ratio of microbubbles results in fast re-dissolution ofthe gas into the water being treated. This rapid re-dissolution allowsthe gas to dissolve into the water before the bubbles have time to risethrough and exit the water column from buoyancy forces, as with otherbubble aeration/oxygenation/ozonation systems. Gas that rises throughand exits the water column is not delivered to where it is needed,resulting in decreased efficiency, increased costs and increasedhazardous conditions (particularly for ozone which can be toxic at arelatively low concentration).

The present invention can provide supersaturated water into a body ofsaturated water. This ability allows the device to provide conditionsand the means for producing nanobubbles (10-100 nanometers diameter)where gas is released at the molecular level into a fluid that cannotabsorb any additional gas. The high shearing action of the carrierstream release through the orifice tube opening coupled with injectionof supersaturated water can produce nanobubbles for applications inmanufacturing, distribution and control of nanoparticles and relatedtechnologies.

Upon leaving the external chamber, supersaturated gas comes out ofsolution in the form of microbubbles that rise much more slowly throughthe water column than larger bubbles from entrainment aeration. The sizeof the orifices, number of orifices per length of tube, and total lengthof the chamber, e.g., diffuser tube, are important considerations,because they can provide flow control for the saturator tank. Thesmaller, slow-rising bubbles generated by the system allow moreretention time in the water column and increase the reach of the oxygenplume downstream from the treatment site in flowing streams.Microbubbles also have high surface to volume ratios that increases theoxygen transfer rate to the water column. The diameter of themicrobubbles can be controlled by controlling the saturation tankpressure, orifice size and location, and the gas mixture.

In a typical use, water is pumped from a locally available source, e.g.,from a stream or water body to be treated, or tap source, and screenedto remove any objects that could damage the device. The inlet water iseither pressurized by passing through a high pressure pump, e.g., apressure increase on the order of 200 psi across pump with a flow ratedependant upon the rate of dissolved gas required, or by other meanssuch as water tower or tap pressure. The pressurized water then passesthrough a high pressure hose and into the top of the saturation tank.Preferably, the water passes through one or more spray nozzles at thetop of the tank and exits the nozzle(s) in mist form into the gasheadspace inside the tank. Water flow can be either continuous orintermittent.

In a convenient mode of operations, the saturation tank includes aliquid layer filling the bottom 75% of the tank and a gaseous headspaceabove the liquid layer in the top 25% of the tank. The gas (air, oxygen,or others) reaches the saturation tank by being released from apressurized vessel (air compressor, bottled gases) or production device(generators, filtration units) and flows through a gas-only pressurehose into the top of the saturation tank. The saturation chamber istypically a stainless steel welded tank cylindrical in shape (0.5 mdiameter, 1.5 m height) oriented perpendicular to the ground withspherical top and bottom end pieces. Sealed input and output ports areconnected to the top and bottom end pieces. The gas is dissolved intothe water within the saturation pressure tank by spraying the water fromthe high pressure pump into the headspace of gas in the top of the tank.The small water particles sprayed from the top of the tank rapidlyadsorb the gas to the point of near-saturation (approximately 95%) atsaturation tank pressure. Typical operating pressure within the tank ison the order of 100 psi but can be controlled to any pressure the devicecan produce and structurally sustain.

The water droplets fall through the gas/spray headspace to the bottomliquid region of the tank to form a seal between the inlet gas and thetank exit. Supersaturated water exits the bottom of the saturation tankthrough an open valve and passes through a high pressure hose until itreaches the orifice tube. The length and diameter of the pressure hoseis sized to deliver the supersaturated water to the desired site in theexternal chamber, e.g., orifice tube, with a minimal pressure drop frompipe friction. The orifice tube is an enclosed vessel capable ofmaintaining a pressure equal to that in the saturation tank (such as arigid pipe section with a welded end cap). Holes of appropriate size andlocation are formed into the walls of the vessel. These holes are theonly egress for the supersaturated water. The orifice tube can be placedat any location where oxygenated water is needed. The tube must beanchored to a solid body if movement of the tube is not desired. Thelocation of the holes in the orifice tube can be tailored to individualapplications (e.g. the holes can force the exit jet of supersaturatedwater to stream to the top of the tube to avoid disturbing the sedimentlayer beneath the orifice tube). Also, a Venturi-type concentricexternal pipe can be placed around the orifice tube for entrainment ofwater being treated to mix with the water being ejected from the orificetube. This allows velocity control of treatment water, improved mixing,and dilution of gas concentration in carrier stream to avoid undesiredeffects of high gas concentrations.

A feature of the saturation tank with a liquid water layer sealing thegas from the exit of the orifice tube requires that the gas (air,oxygen, other) must dissolve into the water before it can exit thechamber. The gas in the headspace above the water region is used tomaintain the pressure within the chamber at a constant value using apressure regulator or other control device at the outlet of the gasstorage vessel. The gas that is not dissolved into the water will bemaintained in the headspace so 100% efficiency of gas utilization isobtained and no gas (often expensive or potentially hazardous) iswasted.

Once the supersaturated water passes through the hole in the orificetube, the pressure surrounding the water drops from saturation tankpressure (typically 100 psi) to ambient conditions (typically near 0 to40 psi gauge). This sudden change in pressure dramatically reduces thesaturated concentration of the gas within the water and the low pressurewater cannot hold as much gas in solution at 0 psi as it could at 100psi. This results in the gas leaving solution in the form ofmicrobubbles. The microbubbles rise in the water column being treatedbecause of the difference in density between the bubbles and thesurrounding water. As the microbubbles rise, oxygen diffuses from thegas bubble in to the surrounding water. Hence, water that has not passedthrough the oxygenator and out the orifice tube is being indirectlyoxygenated by the microbubbles.

The efficiency of the delivery of oxygen (or other gas) from a bubble inwater to solution in the water depends upon the retention time of thebubble in the water and the diffusion length of gas within the bubble.Microbubbles are the most efficient method for delivering oxygen towater since their small size allows them to rise much more slowlythrough the water column (as the viscosity of the water effects smallerbubbles much more than large bubbles), thereby increasing the retentiontime of the bubble in the water column. Also, the smaller the bubble,the shorter the diffusion distance for gas to diffuse to the gas/liquidinterface and pass into solution. Smaller bubbles also increase thesurface area-to-volume ratio allowing the gas/liquid interface todominate the transport of the bubble contents from gas to liquid phaseand greatly increase the rate of dissolution.

Microbubbles can also attach to particulate matter within the water andfloat the particles to the top of the water column. The particulates atthe surface of the water column can be more easily removed by skimming.Also, organic waste in the water column that serves as a source of foodfor bacteria is typically dispersed through the water column asparticulates. Any source of food for bacteria is where bacteria arelocated since microbes will only grow and reproduce in significantnumbers when nutrients are not limited.

The attached microbubble then delivers oxygen directly to the source ofoxygen depletion (bacteria, fungi, or other micro-organism). Also, byfloating the particles to the top of the water column, access to oxygenin the atmosphere at the top of the stream is increased. A shift fromanaerobic to aerobic respiration will allow the organic matter to beconsumed much more rapidly since the kinetics of bacterial respirationprocesses to break down organics to carbon dioxide are far morefavorable to aerobic processes. These respiration processes reducebiological oxygen demand (BOD) of the water and render organicpollutants less damaging. By reducing BOD in the water column, oxygendeficits can be removed as the organic load is reduced to a sufficientlylow level to allow the rate of natural oxygen replenishing processes(such as dissolving oxygen from the atmosphere) in the stream toovertake oxygen consumption rates. Therefore, by treating a water columnimpaired by oxygen deficits from organic loading using the presentinvention, the source of the problem can be removed and repeattreatments may not be required resulting in a long-term sustainablesolution to the impairment.

Potential advantages of the present invention over existing technologycan be summarized as follows:

-   1. The device is portable and can be deployed at remote locations    using a standard gas-powered generator as a source of power.-   2. The device can treat biologically-active water. It utilizes    microbubbles that attach to particulates in the water to quench    oxygen demand at the site of consumption, thus providing rapid    bioremediation response.-   3. The supersaturated water is released from an orifice tube that    can be placed in any location within the depth of a water column and    not just treat the surface (as do agitator-type aerators). This    controlled flow of oxygen-saturated water can provide a curtain of    aeration wherever and whenever desired.-   4. The injection of water with a controlled direction and velocity    does not greatly disturb the water column and sediment as can occur    with entrainment devices such as gas injectors. This avoids    re-suspension of dormant oxygen-consuming particulate in sediment    that can actually increase oxygen uptake in the water column. Mixing    requirements are also reduced as gas dissolved in the water matrix    requires much less energy to distribute than mixing gas with    liquids.-   5. In a closed system reservoir-type water body, the microbubbles    can be pulsed to provide only the amount of microbubbles required to    float algae to the surface of the water column during daylight to    improve photosynthetic oxygen production. At night, the rate of    supplemental oxygen can be increased to make up for the dark    respiration (oxygen consumption) by algae. This cycling can utilize    the net oxygen production of algae as part of the overall    oxygenation system in ponds or reservoirs.-   6. The device adds no chemicals, catalysts, enzymes, or exogenous    materials to the water being treated. Only water, oxygen, or air is    added.-   7. The device is scaleable so the rate of oxygen added can be    increased or decreased to account for highly varying loads of    nutrients. This feature also allows the device to be operated based    on input from a DO sensor, allowing only the required amount of    oxygen be added at the required location.-   8. The device has a low capital cost because no specialized or    expensive equipment is involved.    II: Ozonation of Water

Ozone is, in many respects, the ideal disinfectant. It is easilygenerated on-site, and unlike many other chemical disinfectants, ozonebyproducts (predominantly O₂) have beneficial environmental effects.Ozone increases the dissolved oxygen (DO) concentration of the receivingwater. It also has been shown to effectively oxidize and facilitatehydrolysis of many toxicants in water, including pesticides andtrihalomethane precursors. It also has the added benefit of producingvery few disinfection by-products (DBPs).

Ozone (O₃) is a very effective alternative to chlorination fordisinfection of inactive pathogenic microorganisms. However, ozone isnot broadly used in drinking water or wastewater treatment applicationsbecause of several concerns:

-   1. Ozone is very expensive to generate, and current ozone-water    contactor technology (entrainment) is inefficient;-   2. Current contactor technology (entrainment) results in off-gassing    of ozone due to inefficient uptake, creating hazards for workers and    requiring scrubbing to remove errant ozone; and-   3. Dosage is critical but hard to control with entrainment—low    dosage of ozone may not effectively inactivate some viruses, spores,    and cysts;

The present invention provides for enhanced efficiency of ozone mixingwith bulk liquids. The invention provides ozone to water bodies tooxidize biological and chemical pollutants to improve the effectivenessof water treatment for human contact and consumption. Water treatmentfor drinking water often requires chlorination to disinfect raw water.This chlorine reacts with organic carbon in the raw water entering adrinking water facility, producing disinfection by-products such aschloramines and others, which have been shown to cause cancer. With thepresent invention, ozone can be used to replace chlorination in thedisinfection of raw water. The ability to meter, or control, the dose ofozone being delivered through metered supersaturated waters is a keyinnovation. The invention also provides a mechanism for more accuratelydosing treatment waters for intensive mariculture and aquaculture watertreatment, and for industrial disinfection.

The invention provides ozone to bulk liquids at the molecular andmicrobubble level, thereby enhancing hydrolysis, cell wall lysis, andoxidation. This system can also reduce off-gassing of ozone from thetreated water. This system provides an efficient and safe alternativefor regulatory and safety-motivated disinfection and treatment oforganics. The invention can greatly improve ozonation efficiency. This,in turn, can enhance the economic viability of ozonation as adisinfectant. Specifically, this technology can provide a mechanism toensure that all ozone generated is delivered to the bulk liquid indissolved form, reducing the quantity (thus cost) of ozone necessary fora dose, reducing the need for off-gas collection and scrubbing, andproviding dramatically enhanced dosage control.

Thus, another embodiment of the present invention as shown in FIG. 1,employs an ozone/water saturation chamber under pressure to deliver aflow of supersaturated water for ozonation of bulk liquid. The ozone istypically provided on-site with either an external generator or by agenerator installed within the pressure vessel of the saturation tank.Thus, ozone is delivered to the bulk liquid through a controlled liquidstream that is saturated with a known and controlled amount of dissolvedozone. When the saturated ozone stream is released into the bulk liquidat ambient pressure, the ozone comes out of solution, formingmicrobubbles, and mixes with the bulk liquid. The amount of ozone in thesaturated stream can be controlled by pressure and residence time in thesaturation chamber (flow). Thus, using this technology it is possible tometer ozone to bulk liquids much more precisely, resulting in increasedconfidence of disinfection effectiveness. Off-gassing is greatly reducedbecause all of the ozone contained in the carrier water stream that isinjected into the target water is dissolved. Ozone exiting solution doesso as microbubbles, which quickly absorb into the target water,therefore, preventing off-gassing from bubbles exiting the water columnthrough flotation. Also, since all the ozone produced is stored in asealed tank until it is dissolved into the delivery water stream, nooff-gassing occurs from the device.

Once the supersaturated water stream is injected into the water to bedisinfected, the ozone is released in microbubble form. The microbubblesrise much more slowly through the water column than bubbles producedthrough typical aeration. Microbubbles also have a high surface area tovolume ratio. This increased retention time and surface area coupledwith precise dosage control allows nearly all ozone to be absorbed anddeactivated within the treated water and minimizing release of ozonefrom the top of the water column. This reduces both the costs ofgeneration and the hazards of operation. This aspect of the presentinvention can be scaled for in situ or industrial enhancement of anywater quality processes that could benefit from controlled ozonation.This device allows for the ozonation of water and wastewater sites thatmay otherwise be too costly, such as small water/wastewater facilities,industrial facilities, groundwater remediation sites, and aquaculturefacilities.

For this aspect of the invention, the aforementioned oxygenator ismodified to dissolve ozone in water because of several uniqueconstraints of ozone. Ozone can become explosive at 240 g ozone/m³ air.Operation of the device will not allow ozone to exceed a concentrationof 180 g ozone/m³ air by limiting the pressure that can be formed in thesaturation chamber. Ozone is corrosive to many substances and cannot becompressed with readily available gas compression equipment. Also, ozoneis unstable and compression increases the tendency for O₃ to reduce toO₂. Therefore, ozone cannot be stored in compressed form for anyextended period of time. These constraints require the operation of theozonator to compress ozone immediately after it is generated and quicklydissolve the ozone into water. This can be accomplished through thefollowing operational steps.

-   1. Ozone is produced from dry air at a concentration of 3%.-   2. The initial condition of the saturator is full of water with all    pumps off and outlet valve open. The slightly pressurized ozone    forces the water out of the saturator until there is only a    sufficient amount of water at the bottom of the saturator to prevent    gas from directly exiting the saturator and passing through the    orifice tube.-   3. Once the ozone fills the saturator, the saturator outlet valve is    closed and the ozone inlet valve is closed.-   4. The water pumps are activated, thereby opening the check water    inlet check valve allowing water to enter the spray nozzles and the    saturator.-   5. Water is pumped through the spray nozzles into the saturator    until the water level rises sufficiently to compress the trapped    ozonated gas to the desired pressure. The pressure reached is    limited by the volume of the saturation tank so a working pressure    of 35 psi is the maximum pressure attainable by using water to    compress the ozone.-   6. Once the desired ozone pressure is reached, the water pumps are    turned off (or diverted to prevent excessive motor cycling) which    closes the water inlet check valve to the saturator. The saturator    outlet valve at the bottom of the saturation tank is then opened    allowing the water containing dissolved ozone to exit the saturator    to pass through the orifice tube(s) and create microbubbles to    ozonate the target water to be treated.-   7. The water/ozone solution is allowed to exit the saturator until    the pressure of the ozonated gas in the headspace above the water    decreases to the minimum desired pressure. The saturator outlet    valve at the bottom of the tank is then closed and the water pump is    re-activated to repressurize the system.-   8. Ozone does not need to be added to the saturator until the    concentration of ozone in the headspace is reduced below a critical    level due either to dissolution in water or reduction in    concentration by conversion to O₂. As the concentration of ozone in    the gas headspace is reduced, the pressure of the headspace can be    increased without danger of explosion. This allows the rate of ozone    added to the treatment water to be held constant even though the    saturator pressure and ozone concentration in the headspace are not    constant.-   9. Once ozone concentration in the gas headspace in the saturator is    reduced below an effective level, the fill/empty cycle can be    modified by pressurizing the saturator by pumping water into the    saturator through the spray nozzles until the headspace is    compressed to the maximum allowable pressure or the saturation    chamber is filled with water. The water pumps are turned off and the    outlet valve opened to release pressure to below that of the ozone    generator outlet. Then the ozone entry valve is opened allowing    ozone to refill the saturator and the fill/empty cycle is repeated.-   10. To obtain near-constant delivery rates of water supersaturated    with ozone several saturation chambers can be operated in parallel    with a time offset.

The advantages of an ozonator according to the principles of the presentinvention compared with previous technology are summarized as follows:

-   1. The ozonator is compatible with current ozonation infrastructure,    requiring minimal retrofitting.-   2. The ozonator treats biologically-active water. It utilizes    microbubbles that attach to particulates in the water to disinfect    both suspended and flocculated pathogens.-   3. The supersaturated water is released from an orifice tube that    can be placed in any location within the depth of a water column.    This controlled flow of ozone-saturated water can provide a curtain    of disinfection wherever and whenever desired. No off-gassing    occurs, so scrubbers may not be necessary, potentially reducing    installation and operation costs and increasing safety.-   4. The injection of water with a controlled direction and velocity    provides for greatly enhanced dose and residence time control,    critical elements for effective and efficient ozone disinfection.-   5. The device adds only ozone and adds no other chemicals,    catalysts, enzymes, or exogenous materials to the water being    treated.-   6. The device is scaleable so the rate of ozone added can be    increased or decreased to account for highly varying bulk liquid    volumes and particulate concentrations in the liquids being treated.    This feature also allows the device to be operated based on input    from a turbidity and ORP sensor set, allowing only the required    amount of ozone be added at the required location automatically.-   7. The device has a relatively low capital cost because no    specialized or expensive equipment is involved.

The present invention is now described with reference to particularexamples, which are presented to illustrate the invention, but do notlimit it.

EXAMPLES Example 1

Oxygenation with Air or Oxygen

A proof-of-concept system was constructed and preliminary“proof-of-concept” testing performed using a 1000-gallon capacityplastic tank filled with water containing varying levels of organicpollutants to simulate field conditions. The results of some of thepreliminary tests performed are summarized hereinbelow.

Tap water with added sodium sulfite (an oxygen binder) was treated toraise DO from 1 mg/liter to 6 mg/l. Oxygenation rates measured were:bubble aeration 9.1 g oxygen/hr, oxygenator with air 22.7 g oxygen/hr,oxygenator with oxygen 113.6 g oxygen/hr. Energy to oxygenate the tankwater using oxygen and the oxygenator was ⅙ that of bubble aeration.Weak animal lagoon water was added to the treatment tanks. Test resultsindicated the oxygenator was able to create a floating layer of algae,and supersaturated DO conditions were maintained throughout the test.The bubble aeration tank created turbulence that continually fracturedthe algae layer.

Food-processing waste was added to the tank. Indigenous microbes grewrapidly causing the wastewater to have a measured pretreatment DO nearzero. The oxygenator was able to quickly increase DO to above saturationlevels (7 mg/liter) and remove all objectionable odor very quickly.

The optimum operating parameters determined to maximize the ratio ofoxygenation rate to power consumed in non-bioactive reduced DO tap waterwere first determined using the field-scale oxygenator (nominal waterflow rate of 20 gallons per minute). When the maximum energy efficiencyfor the field-scale unit was determined to be the minimum nozzle size (1nozzle) and maximum pressure (100 psi), the test was repeated using thelab scale oxygenator (nominal flow rate 2.7 gallons per minute) where aslightly higher pressure and smaller size nozzle could be used.

This experiment was conducted to determine the overall effect ofsaturation chamber pressure, and nozzle size on the efficiency of oxygendelivery in terms of rate of oxygen delivered per energy consumed (goxygen per minute per kW electricity consumed). The higher thesaturation tank pressure, the higher the partial pressure of oxygen inthe gas (air) and the more oxygen that can be dissolved into the waterin the saturation chamber. However, this increase in oxygen delivery iscounteracted by an increase in energy cost since the pump must providemore work to deliver water to the saturator at a higher pressure. Also,as the size of the nozzle decreases, the backpressure against the pumpincreases, which results in higher pump energy consumption. However, asthe nozzle size decreases, the water spray entering the saturationchamber is increasingly atomized and the percent oxygen saturationincreases.

The field-scale oxygenator was set to deliver water into the saturatorat pressures of 40, 60, 80, and 100 psi. The nozzles were arranged to betested using 1, 2, 3, and 4 nozzles in parallel (in effect increasingthe nozzle diameter and decreasing backpressure with more nozzles). Twotests at each setting were completed and all tests were conducted inrandom order blocked within number of nozzles (it is cumbersome tochange nozzles). Compressed air was used as the gas. Water flow rateswere measured as the oxygenator delivered microbubbles to deoxygenatedwater (using 300 grams sodium sulfite to reduce DO to less than 1.0mg/L) in a 1000 gallon tank. Inlet water to the oxygenator was alsodeoxygenated so the only oxygen added to the system was from theoxygenator. DO and temperature were measured using 2 duplicatecalibrated YSI-85 probes in the treatment tank. Each test was conductedover a time period of 15 to 30 minutes depending upon the water flowrate into the treatment tank. Tests were ended when water DO exceededsaturation at atmospheric conditions. Energy consumption was monitoredby measuring electrical current and voltage for the pump.

Once all data was collected for tests, a first order equation was usedto model the DO in the tank as a function of time. The model was usefulto calculate the rate of oxygen delivered for all tests at referenceconditions for water temperature and initial water DO, which wereslightly different between tests. The first order equation is:DO _((any time))=(DO _(initial) −DO _(final))exp(−k*time)+DO_(final)  (1)

The parameters of k (first order constant) and DO_(final) were fitted tothe data using a least squares error method. Average error of predictionwas very small at 2%. DO readings were all converted to percentsaturation at atmospheric pressure and then back to DO at a standardizedtemperature of 20° C. Also from this data, the rate of addition ofoxygen is reduced with time as the DO of the tank increases and thegradient between DO of treatment water and DO of tank water decreases.This phenomenon does not likely occur during treatment of streams as thewater being treated will remain at a constant, low DO since the processwill be continuous flow. To represent this effect, the rate of oxygenadded to the tank was computed using the first order model (equation 1)with k and DO_(final) computed from each test assuming an initial DO of1.0 and treating for 1 minute for all tests. Again, this was done tostandardize comparisons. The total oxygen added over this minute wasassumed to be the rate (g oxygen per minute) added to each tank.

Energy consumption was determined from the equation for energy deliveredto the system, not energy actually consumed by the motor. This was doneso comparisons can be made between systems of different scale usingdifferent pumps. The computation for energy delivered to the system doesnot include any inefficiencies incurred by the electrical motor. Motorefficiencies can vary widely and can greatly skew comparisons betweenoxygenators at different scales. For example, the field scale unit usesa centrifugal booster pump with motor with an efficiency of around 50%.The lab-scale oxygenator uses a piston displacement pump with a motor20% efficient. If the rate of oxygen delivered per kW energy consumed bythe motors were calculated, the field-scale unit may measure to besignificantly better than the lab scale even if the number of nozzlesand pressure settings result in exactly the same performancecharacteristics with the difference being because of the motor only.This problem can be solved by resizing the motor or changing the pumptype, without changing the nozzle and pressure configuration.

The energy delivered by the oxygenator is given by:E=Backpressure on pump*Flow rate  (2)

Both of these parameters were measured during the tests and efficiencywas determined by dividing standardized rate of oxygen delivered byenergy delivered. Results are shown in FIG. 2.

The highest efficiency (near 2.7 g O₂ per kW) for the field-scale unitwas obtained using the highest setting of saturator pressure (near 100psi) with the fewest number of nozzles (one). This result indicates thatif the nozzle size could be reduced and the tank pressure increased,efficiency may increase. The effect of nozzle size on the percentsaturation of water in the saturation chamber was also analyzed usingthe data above. The nozzles used in the field-scale unit were TF fullcone-type, 2F-20, 120° pattern, brass nozzle (BETE Fog Nozzle, Inc.) andthe nozzles used in the lab-scale unit were wash jet-type, #25, 15°spray pattern (Spraying Systems Co.; Wheaton, Ill.). As nozzle sizedecreases, the water spray into the saturation chamber is increasinglyatomized and backpressure behind the nozzle increases.

FIG. 3 shows the effect of increased nozzle backpressure on the percentsaturation of water in the saturation chamber. The saturation chamberpressure is held constant at the desired set point in these experiments.The smaller nozzles in the lab-scale unit were able to increasesaturation efficiency to nearly 100% at some of the testing points. Thisindicates the type of nozzle used is important for optimizing the rateof gas dissolved in the liquid per power consumed. A suitablecommercially available nozzle can be obtained from Spraying Systems Co.(Wheaton, Ill.).

The effect of saturation tank pressure on efficiency of oxygen deliverywas explored for the two nozzle sizes in the lab-scale unit. It waspossible to achieve higher saturation tank pressures with the lab-scaleunit. Both nozzle sizes were able to achieve peak efficiencies close to4.5 g O₂ per kW, which is a substantial increase over the field-scaleunit with less optimal nozzles.

Example 2

Comparison of Oxygenator with Other Devices

A device of the present invention was compared to currently usedtechnology for providing oxygen to wastewater. The most commonly usedtechnologies are fine-bubble aeration provided through diffusers byblowers or compressors using atmospheric air (fine-bubble air) orcompressed oxygen (fine-bubble oxygen).

Mixed Liquor was obtained from the Fayetteville, Arkansas wastewatertreatment plant. The wastewater was stored in a 550 gallon plastic tankuntil used in these tests. The mixed liquor quickly become anaerobic andremained so until testing. Each test began by transferring approximately100 gallons of the mixed liquor into an open-top 1000 gallon tank. Then700 gallons of reduced DO tap water (sodium sulfite was used to removeoxygen) was added. The wastewater solution was then mixed using a sumppump turned on its side. Two calibrated YSI-85 DO probes were placedinto the wastewater and initial samples were collected at two hourintervals for Specific Oxygen Uptake Rate (SOUR), solids, and BOD5(dissolved oxygen consumed in 5 days by biological processes). Anoxygenator according to the present invention was operated at asaturation tank pressure of 110 psi with one small nozzle. The standardair and oxygen fine-bubble systems (obtained commercially from SanitaireCorp. (Brown Deer, Wis.) were operated by providing compressed gas intoa rubber diffuser that is commonly used in the wastewater aerationindustry. The flow rates for standard bubble aeration were 15 L/min foroxygen and 34 L/min for air.

The equipment tested (oxygenator, standard bubble aeration, standardbubble oxygenation) was operated until the DO in the tank reached 7.0mg/l. At this point, the equipment was turned off and remained off untilthe DO dropped to 5.0 mg/l. This sequence of operation (FIG. 4) wascontinued for 8 hours and ensured that each piece of equipment need onlybe operated at its minimum duty cycle to provide adequate oxygen(5.0-7.0 mg/l) for biological treatment to occur.

Specific oxygen uptake rate (SOUR) and 5-day biochemical oxygen demand(BOD5) were measured during treatment of wastewater using standardmethods (APHA, 1998). The results show that, as expected, if sufficientoxygen is provided, the biological processing to remove BOD will occur.SOUR is the rate of oxygen consumed per mass of volatile solids.Volatile solids indicate mass of bacteria and SOUR indicates theactivity of the bacteria consuming the solids. Bacteria found inmunicipal wastewater treatment systems have been carefully evolved overtime to provide the most efficient treatment of BOD. When the oxygendemand of these bacteria is met, they quickly reduce their consumptionper mass. This data indicates a typical result when “stale” bacteria areused in a batch process (the bacteria are stale since they were storedfor several days and allowed to become anaerobic). The BOD5 dataindicates significant reduction has occurred in all three treatmentsand, as expected, by providing sufficient oxygen to the system, thedesirable biological processes can occur. Based on the BOD data, thetime to reduce the BOD in each tank was estimated by determining theamount of remaining BOD that needed to be removed after the 8 hourtreatment and determining the rate of reduction of BOD for eachtreatment based on the 8 hour test. The time remaining was added ontothe 8 hours for an estimate of the total time required. The dataavailable to make these estimates is limited, so cost comparisons per 8hour basis were also made.

The source of oxygen was a 4 foot compressed oxygen cylinder with avolume of approximately 42 liters. The source of air was a 4 footcompressed air cylinder. Since compressed gas cylinders were used, nosource of electricity was required for the fine-bubble system. Oxygenand air from these cylinders is much more expensive than can be acquiredfor larger scale operations. Air in particular is much cheaper if ablower or compressor is used directly. However, the air flow ratesrequired for this test were beyond the capability of any available andaffordable compressor units and a cylinder was used. The costs forproviding 34 L/min of compressed air with a 5 hp compressor can beestimated from US DOE, Industrial Technology Program Compressed Air TipSheet #1

(www.eere.energy.gov/industry/bestpractices). The costs of using thiscompressor on the test system are estimated below for a more reasonablecomparison to fine-bubble air systems.

Cost data showed a large savings provided by an oxygenator of thepresent invention, with the treatment level provided at least equal tothat of the other treatments. The estimated time to reduce BOD5 by 50%was slightly less for the present invention (lab scale) compared withstandard bubble aeration. It is believed that alternative systems wouldbe deemed feasible if a 15% to 40% reduction in cost were achieved. Thisobjective was exceeded when the oxygenator was shown to achieve an 83%reduction in cost (see Table 1). TABLE 1 Comparison of three O₂ deliverytechnologies by efficiency and cost. Standard Present Standard bubbleInvention bubble aeration oxygenation O₂ delivery rate 156 g O₂/hr 6.4 gO₂/hr 27 g O₂/hr Rate of energy 0.956 kW 3.7 kW 0.0 kW consumption(estimated for properly sized 5 hp blower) Average Cost $0.41/hr$4.00/hr $1.96/hr Oxygen or Air (air cylinder) (cylinder) ActualOperating time of 0.54 hr 5.65 hr 3.35 hr device over 8 hr test ActualCost to Oxygenate $0.25 $22.60 $6.57 for 8 hrs (cylinder) (cylinder)(electricity $0.06/kW-hr) $1.27 (Estimated Blower) Estimated Time to16.5 hr 19 hr 30 hr Reduce BOD by 50% based on Observed Rates EstimatedCost to Reduce $0.52 $53.68 cylinder $24.64 BOD by 50% $3.02 CostSavings % — 99% cylinder 98% 83% estimated blower

The present invention was compared to surface impeller and dropstructure treatment. These are technologies often used to treat highstrength wastes that would be typical of those generated at an animalproduction or food processing facility. A surface impeller is a devicethat agitates the surface of a pond or tank to increase the amount ofoxygen from air dissolved into the wastewater through physicalentrainment. A drop-structure uses the potential energy of flowing waterto fall through air and create agitation at the surface which increasesthe surface area of wastewater exposed to ambient air and mixes in airvia entrainment when the water drops through the surface. The agitatorwas ¾ horsepower rotating shaft with an impeller. The drop structureused a pump to circulate the wastewater to an elevation of 4 feet abovethe water surface at the drop point. The flow rate of the pump was 120liters per minute. The present invention was used at a saturation tankpressure of 110 psi with one small nozzle.

The wastewater used for these tests was obtained from a hog house manurepit located at the University of Arkansas Swine Research Facility inSavoy. The liquid waste was stored in a 550 gallon plastic tank untilused. The waste quickly become anaerobic and remained so until testing(16 days). Testing with each aeration technology began with setup of theequipment and instrumentation. Approximately 70 gallons of manure wereadded to 730 gallons of water in a 1000 gallon tank to provide amoderately high strength wastewater (BOD5 of about 750 mg/l). Thewastewater had relatively high concentrations of ammonia (>120 mg/l) andphosphorus (>25 mg/l), but low concentrations of nitrate (<1.0 mg/l) atthe start of testing. Aeration testing was conducted for 8 hours withfrequent sampling of DO, BOD5, SOUR, temperature, and nutrients.

Calibrated DO probes (YSI-85) were placed into the water and testingbegan. The equipment was operated until the DO of the water reached 7mg/L at which point the equipment was turned off. Operation began whenthe DO of the water dropped below 5 mg/L. Dissolved oxygen data areshown in FIG. 5. As occurred with the mixed liquor tests, an oxygenatoraccording to the present invention was able to provide oxygen to thesystem much more rapidly than either surface agitation or the dropstructure.

Samples for BOD5, SOUR, and solids were collected at elapsed times of 0,0.25, 1, 2, 4, and 8 hrs. Each of these tests was replicated for a totalof two tests using each technology. The BOD5 and SOUR data indicatesthat the swine waste was very strong wastewater and provided a stem testfor the technologies. The BOD5 and SOUR data also indicate that typicalbiological treatment is occurring for all tests as these measures aredecreasing, albeit slightly. These experiments were conducted outdoorsand the wastewater temperatures were near 10° C., so biologicalprocessing of BOD was expected to be slow. The wastewater temperaturebetween treatment tests was difficult to control, so temperaturecorrection of all process rates to a normalized value at 20° C. was madeusing the method of Chapra (S. Chapra, 1997, Surface Water-QualityModeling. WCB/McGraw-Hill, Boston, Mass.).

Time to reduce BOD5 by 50% was estimated from the test data. BOD removalrates were standardized to 20° C. for computation of total treatmenttimes in Table 2. The oxygenator data indicated an average time savingsof removing 50% of BOD of 38.9% under surface agitation and 19.9% underdrop structure treatment. These savings meet the criteria established inobjective 3 of 15-40% savings for success. These data contain muchvariation because of the variation in BOD in the raw wastewater. It isnoted that the swine wastewater data show much more variation than therelatively processed and consistent mixed liquor. TABLE 2 Rates ofreduction of BOD from each treatment process % Reduction Rate ofReduction Est'd Time BOD5 SOUR BOD5 SOUR to Reduce Treatment (%) (%)(%/hr) (%/hr) BOD5 (hr)* Agitation R1 4.0 4.17 0.5 0.521 72.8 AgitationR2 15.4 2.25 1.9 0.281 17.9 Drop Structure R1 0.8 1.57 0.19 0.197 190.0Drop Structure R2 9.2 4.58 1.1 0.573 33.1 Eco-Oxygenator R1 7.4 2.50 0.90.312 37.7 Eco-Oxygenator R2 15.2 3.92 1.9 0.490 15.3*Estimated time to reduce BOD5 50% 20 deg C.

Ammonia (as ammonium), dissolved phosphorus, nitrate, and nitritesamples were collected at the end of each test. Nutrient dynamics acrossall treatments were as expected for bio-solids that were converting fromanaerobic to aerobic respiration and growth processes (Table 3).Nitrites increased in each case, even doubling in the drop structuretreatments, reflecting a probable oxygen limitation in thebacterially-mediated nitrification process that converts ammonia tonitrate. Nitrates decreased in four of the six trials, and eachtreatment process reduced ammonia by between 2 mg/L (2%) and 21 mg/L(13%). Phosphorus uptake was highest in the drop structure, and lowestin the oxygenator. Nutrient dynamics observed in treatment of this highstrength waste reflect microbial uptake processes, and thus are rathervariable, given the size of the test system. The oxygenator does notappear to reduce these pollutants any more effectively than othertechnologies. However, it is clear that the oxygenator aeration systemwas approximately as effective at supporting microbial dynamics as theconventional treatment systems. TABLE 3 Summary of nutrient reductionsin two replications of each treatment. Nutrient Reductions (mg/l/%) byAeration Processes Oxygenator Agitation Drop Structure Parameter Rep 1Rep 2 Rep 1 Rep2 Rep 1 Rep 2 NO₂—N  0/0 −0.05/−41  −0.05/−67  −0.02/−23  −0.07/−115  −0.06/−100 (Nitrite) NO₃—N 0.06/11  0.02/5.1 0.12/25   0/0−0.05/−12 0.06/12 (Nitrate) NH₄—N 10.2/4.4 10.4/8.3 2.13/1.8 3.44/2.621.3/13  8.70/5.7 (Ammonium) PO₄—P −0.28/−1.0 0.09/0.4 2.39/8.6 1.57/5.74.99/17 3.36/13 (Dissolved Phosphorus)(note (−) means increase in nutrient)

Treatment costs were compared and, again, the oxygenator showed asubstantial cost savings. When actual costs were compared for conductingthe 8 hour tests, substantial costs savings were computed. Operatingcosts and time to reduce BOD5 by 50% are shown in Table 4 hereinbelow.

Example 3

Field Deployment

The field-scale oxygenator was deployed at two locations in NorthwestArkansas:

Mud Creek and Columbia Hollow Creek. Measurable increases in DO weremeasured at both locations. The deployment at Columbia Hollow Creek alsodemonstrated substantial reductions in BOD5 and ammonia levels. Theability to float suspended solids for subsequent removal by skimming wasalso demonstrated at this location.

The initial deployment was conducted in Mud Creek in Fayetteville, Ark.at a point just before the confluence of Mud and Clear Creek. A majorityof water in this stream under base-flow conditions is effluent from theFayetteville Wastewater Treatment Plant. During rainfall events, most ofthe flow is urban runoff from the City of Fayetteville. This stream isclean with a low BOD and acceptable DO. TABLE 4 Comparison of threeaeration technologies in terms of time and cost Present SurfaceInvention Agitation Drop Structure Rep 1 Rep 2 Rep 1 Rep 2 Rep 1 Rep 2O₂ delivery rate (g O2/ 184 101 21 13 13 16 hr) Power (kW) 1.08 0.9650.589 0.583 1.089 1.085 Average Cost 0.48 0.26 — — — — Oxygen or Air($/hr) @ $0.00218/ liter Operating time over 8 hr 0.173 0.168 3.97 4.1257.43 5.083 test Total Cost ($) 0.0943 0.0534 0.14 0.144 0.485 0.331(electricity $0.06/kW-hr) Ave Actual — — 74.0 81.9 Cost Savings (%)Estimated Time 37.7 15.3 72.8 17.9 190 33.1 to Reduce BOD (not 50% (20°C.) used) Ave Time — 38.9 19.9 (rep 2 Savings of Eco- only) Oxygenator(%)

The oxygenator was installed on the stream bank and the orifice tubeplaced in a deep pool (depth of 2 feet) within the stream. Mud Creek hada flow rate of 9 cubic feet per second measured prior to deployment.This flow rate varied greatly as several rainfall events occurred duringdeployment. Since the watershed is urban and mostly paved, the streamflow rate can change very quickly during rain.

The In Situ TROLL 9000 (Fort Collins, Colo.) datasondes were anchored tothe streambed at 4 locations: just upstream from the orifice tube, 30yards downstream, 120 yards downstream, ¼ mile downstream. Thedatasondes were calibrated in the lab prior to deployment and programmedto monitor DO, temperature, and water depth. Oxygen cylinders were usedto supply the gas. Saturation tank operating pressure was limited to 80psi because of vortexing problems. Two nozzles were used (this practicedeployment was done prior to completion of the optimization tests). Theoxygen injected into the stream was clearly visible surrounding theorifice tube.

Once proper operation of the unit was established, the stream wasoxygenated over a period of 37 hours before a large rainfall event (at87.5 hours) occurred and flooded the stream (stream depth rose 4 feet).The control site upstream from deployment and 120 yard site datasondeswere recovered and the results are shown in FIG. 10. From this data, anaverage increase in DO content of the stream of 1.14 mg/l at the 120yard site was realized. The oxygenator was not operated continuouslyduring the 37 hours as oxygen cylinders needed to be manually changed asthey emptied. The 120 yard site DO is consistently higher than thecontrol site. The time lag between the two sites has been removed sothat the DO values indicated represent approximately the same water. Thelag time was established by average stream flow velocity and knowing thedistance between the sites.

Over the 37 hour test period, the rate of oxygen used from the cylinderwas approximately 27.7 g/min. If it is assumed that all this oxygen isadded to the stream and the stream flow rate is assumed to be around 10cubic feet per second (or 16,990 liters/min), then the rate of oxygenadded should increase water DO by 1.6 mg/liter. The actual increase wasless than this value (1.14 mg/L). This result seems reasonable sincesome oxygen would have been consumed by biological oxygen demand withinthe stream. Costs of operation for oxygenating the stream in this testwere $120 for oxygen, and $130 for gasoline for generators for a totalof $250. The rate of cost was $0.0038 per gram oxygen delivered. As acomparison, the cost of operating the lab-scale unit is similar at$0.00296 per gram.

The second field deployment was conducted at Columbia Hollow Creek inBenton County, Ark. This stream is highly impacted with organic wastesand possesses a significant BOD. The stream was sampled for waterquality parameters including BOD5, DO, ammonia (indicated by ammonium),nitrate, nitrite, and soluble phosphorus. In Situ Model 9000 Datasondeswere placed at 4 sites in the stream: site 1 was upstream of theoxygenator deployment site; site 2 was 100 feet downstream from theoxygenation site; site 3 was 1000 feet downstream from the oxygenationsite; and site 4 was 2000 feet downstream.

Datasondes collected DO and water temperature for 3 full days prior tooxygenator deployment (Aug. 12-14, 2004) to gather baseline data. Theaverage baseline DO content was 5.35 mg/l at site 1, 4.48 mg/l at site2, 3.45 mg/l at site 3, and 2.67 mg/l at site 4.

After the 3 day baseline measurements were collected, the datasondeswere removed from the stream, recalibrated, and redeployed into thestream. During the redeployment, the datasonde located at site 2 wasbroken and unusable for further data collection. Oxygen concentrationwas manually measured (using a YSI-85 DO probe) at Site 2 periodicallythroughout the rest of the experiments. The oxygenator was activated andoperated for 7 hours (noon-7 pm) at full capacity; this is referred toas treatment 1. The second oxygenation (treatment 2) was conducted onday 2 for 6 hours. Oxygenation was conducted for 6 hours on day 3(treatment 3) and 8 hours on day 4 (treatment 4).

The oxygen mass balance of the stream system is extremely complex andcan only be roughly estimated. Oxygen is added to the stream fromambient air and algae photosynthesis and removed by respirationprocesses by living matter in the water and sediment. The assumptionsmade to estimate the increase in DO from deployment of the oxygenatorare grossly simplified, but do provide useful information. The change inoxygen concentration in stream water because of oxygenation can beestimated by subtracting the DO at the site in question from theupstream site for data collected prior to oxygenation. This is referredto as the baseline difference. If the baseline difference is subtractedfrom the average DO value at the upstream site during the oxygenatortreatment, this result should estimate the DO of the site in question ifthere were no oxygen added. The difference between this result and theactually measured DO then estimates the increase in DO from theoxygenator. The DO at site 2 was measured manually using a YSI-85 meter.Manual readings were not collected during treatments 1 and 2. The dataare shown in Table 5. TABLE 5 Estimated increase in DO (mg/L) fromOxygenator treatment Increase in DO (mg/L) by Treatment Treatment 1Treatment 2 Treatment 3 Treatment 4 Site 2 (100 ft) — — 2.43 3.07 Site 3(1000 ft) 1.22 0.62 0.84 1.27 Site 4 (2000 ft) 0.49 1.23 1.11 0.73

In addition to measuring an increase in DO from oxygen added by theoxygenator, a reduction in BOD5 is also indicative of an improvement ofthe health of a stream. The average oxygen uptake rate measured for thewater in Columbia Hollow Creek prior to deployment was 4.43 mg oxygenper liter per day (similar to a BOD5 of 22.2, which is quite high). Thisstream had a high level of stored oxygen consumptive capacity and it wasassumed that a portion of the added oxygen would be quickly consumed.Therefore, BOD5 comparisons were made between site 1 (the control siteupstream from deployment) and site 2 (100 ft downstream fromdeployment). Prior to deployment during the four treatment days theaverage natural variation in BOD5 was a decrease of 0.25 mg/L betweensite 1 and 2. During deployment, the reduction in BOD5 between thecontrol site and site 2 100ft. downstream from deployment was an averageof 10.1 mg/L for the four treatments for an average estimated reductionin BOD5 of 9.85 mg/liters. Therefore, this data indicates that part ofthe oxygen provided by the oxygenator initiated a substantial reductionin BOD5.

Nutrient data was collected at each site, and because of the widevariance in ammonia, nitrate, nitrite, and phosphorus in the effluent,it was difficult to discern the effect of oxygenation on thesepollutants. However, a 50% reduction in ammonia (NH₄) levels duringoxygenation was measured between site 1 (the control site upstream fromdeployment) and site 2 (110 ft downstream from deployment). Thisreduction was not observed in the baseline data before or one week aftertreatment. It can be theorized that this reduction in ammonia levels wasdue to rapid oxidation in the presence of dissolved oxygen. Otherobservations from these deployments were that the oxygen microbubblesprovided flotation of what appeared to be sludge from the stream. Thisfeature would allow for the removal of suspended solids by skimming.

In summary, an oxygenator according to the present invention was able toprovide oxygen to the highly impaired Columbia Hollow Creek andmeasurements indicate an increase in the DO content, a decrease in BOD5,a reduction in ammonia levels and flotation of suspended solids.

The present invention has been described hereinabove with reference tocertain examples for purposes of clarity and understanding. It should beappreciated by the skilled practitioner that certain modifications andimprovements to the invention can be practiced within the scope of theappended claims and equivalents thereof.

1. An apparatus for dissolving a gas in a liquid comprising: (a) asaturation tank comprising (i) a pressure vessel for containing theliquid and providing a regulated gas head space above the liquid, (ii)at least one liquid spray nozzle that permits passage of liquid into thepressure vessel, and (iii) an outlet for the liquid; (b) liquid pumpingmeans in fluid communication with the at least one liquid spray nozzle;(c) a source of the gas in communication with the regulated gas headspace of the saturation tank; and (d) a chamber external the saturationtank and connected thereto via the liquid outlet, which chamber isprovided with a plurality of orifices through which liquid containingdissolved gas from the saturation tank can be released into a regionexternal the chamber.
 2. The apparatus of claim 1, wherein said regionexternal the chamber has a lower pressure than internal the chamber, sothat the saturation concentration for the dissolved gas in liquidexiting the chamber is exceeded and microbubbles of gas are formed at ornear the chamber orifices.
 3. The apparatus of claim 2, wherein themicrobubbles have an average diameter less than about 150 microns. 4.The apparatus of claim 1, wherein the gas is selected from the groupconsisting of air, oxygen, ozone, hydrogen, nitrogen, nitrous oxide, andcarbon dioxide.
 5. The apparatus of claim 1, wherein the liquidprimarily comprises water.
 6. The apparatus of claim 1, wherein thepressurized pumping means is provided by (i) a high pressure liquidpump, (ii) a line source in a residential or industrial setting, or(iii) a plurality of fixed volume vessels capable of forcing liquid intothe saturation tank upon pressurization of the fixed vessel with a highpressure gas that enters the vessel and displaces the liquid through anoutlet in the vessel.
 7. The apparatus of claim 1, wherein the ratio ofliquid volume to head space gas volume in the saturation tank ismaintained with an open-loop or closed-loop control system.
 8. Theapparatus of claim 1, wherein the number, size, and placement oforifices in said chamber are predefined so as to permit the rate ofliquid flow rate out of the chamber to balance the rate of liquid flowinto the saturation tank, thereby maintaining a constant desiredpressure internal the saturation tank under constant flow conditions. 9.The apparatus of claim 1, wherein the orifices have a diameter in therange of about 1 mm to about 15 mm.
 10. The apparatus of claim 1,wherein said chamber is provided internal a liquid entrainment means, sothat the liquid containing dissolved gas exiting the chamber mixes withlower pressure ambient liquid.
 11. The apparatus of claim 1, wherein thegas saturation threshold for the liquid is thermally controlled.
 12. Theapparatus of claim 1, wherein said at least one spray nozzle isadjustable so as to optimize the liquid droplet size and control therate of gas saturation in the liquid.
 13. The apparatus of claim 1,wherein the source of gas comprises means for separating oxygen fromambient air.
 14. The apparatus of claim 1, wherein the source of gascomprises an ozone generator provided internal the saturation tank. 15.The apparatus of claim 1, further comprising a control system forcontrolling operation of the apparatus.
 16. The apparatus of claim 1,further comprising a feedback loop that permits recovery and recyclingof the gas to the saturation tank.
 17. A method of dissolving a gas in aliquid comprising: (a) pressurizing an enclosed vessel with the gas; (b)spraying a first portion of the liquid into the vessel containing thegas under conditions effective to dissolve the gas in the liquid; (c)passing the first portion of liquid containing dissolved gas from thevessel into a chamber that is provided with a plurality of orifices andwhich is immersed in a second portion of the liquid; and (d) dischargingthe first liquid portion containing dissolved gas through the chamberorifices into the second liquid portion.
 18. The method of claim 17,wherein said pressurizing is conducted with a gas selected from thegroup consisting of air, oxygen, ozone, hydrogen, nitrogen, nitrousoxide, and carbon dioxide.
 19. The method of claim 17, wherein saidspraying is performed with a liquid primarily comprising water.
 20. Themethod of claim 17, wherein said spraying is performed until the firstportion of liquid is dissolved with gas to 95% of saturation at theenclosed vessel pressure.
 21. The method of claim 17, wherein the gas isseparated on-site from ambient air prior to being pressurized into thevessel.
 22. The method of claim 17, wherein said pressurizing isconducted with ozone gas.
 23. The method of claim 17, wherein the gas isprovided by on-site generation.
 24. The method of claim 17, wherein theliquid is provided by a water tap located in a residence or industrialsite and liquid is transferred into the vessel under tap pressure. 25.The method of claim 17, which is performed in continuous mode.
 26. Themethod of claim 17, wherein the liquid is sprayed into the vessel underpressure provided by a high pressure liquid pump.
 27. The method ofclaim 17, wherein fluid flow into the vessel from a high pressure pumpis controlled via feedback from sensors indicating water capacity withinthe saturation tank.
 28. The method of claim 17, wherein saiddischarging of liquid containing dissolved gas is effective to: (i)enhance microbe growth and respiration rate in waste water treatment,fermentation processes, food synthesis and manufacturing, or solid wastetreatment; (ii) promote physical flotation of matter suspended in theliquid; (iii) quench anaerobic biological activity in the liquid; (iv)produce nanobubbles (10-100 nm diameter); (v) foam a polymer; (vi)create a biorefuge for attracting or sustaining fish populations; (vii)sterilize a body of water; (viii) facilitate surface freezing whileaerating/oxygenating during cold weather; (ix) to control odor,antibiotic residuals, and/or bacterial loads in sewage transportconduits; (x) improve the quality of water entering, transducing, orexiting a darn; (xi) improving aerobic digestion efficiency and/or odorcontrol in a wastewater treatment pond (lagoon); (xii) respond to apollutant spill into an environmental water body; (xiii) isolate and/ortreat a plume of pollution; (xiv) disinfect and reduce organic carbon indrinking water; (xv) control aerobic and anaerobic conditions inbiological processes associated with pharmaceuticals and biotechnology;(xvi) deliver hydrogen or other gases to create and control aerobic andanaerobic conditions in biological processes associated with in situwaste treatment in groundwater; (xvii) deliver hydrogen or other gasesto create and control aerobic and anaerobic conditions in biologicalprocesses associated with in situ waste treatment in surface waters;(xviii) deliver a high concentration of dissolved oxygen to enhancebiological oxidation of organic carbon and nitrogen removal withinwastewater treatment facilities; (xix) oxidize sediment in situ forenhanced bioremediation of contaminants sorbed to and associated withriver, lake, and estuarine sediments; (xx) enhance oxygen treatment ofrefractory pollutants such as antibiotic residuals, endocrinedisruptors, pesticides, and similar chemicals; (xxi) enhance ozonetreatment of refractory pollutants such as antibiotic residuals,endocrine disruptors, pesticides, and similar chemicals; (xxii) injectsupersaturated stream of oxygen, ozone, hydrogen or other gases fordirect treatment or enhancing treatment of groundwater to removepollutants; (xxiii) increase the rate of BOD removal because of improvedtreatment rate from smaller bubble size; or (xxiv) increase thethickness of the aerobic layer in sediment for increase storage capacityof phosphorus or other water pollutants.